Video: Estimating the Measure of an Angle

Tim Burnham

Which of the choices is closest to the size of angle 𝐵𝐴𝐶? [A] 126° [B] 48° [C] 228°.

01:33

Video Transcript

Which of the choices is closest to the size of angle 𝐵𝐴𝐶?

Now to identify which angle we’re talking about, 𝐵𝐴𝐶 tells us about the journey that we have to make, so we go from 𝐵 to 𝐴 to 𝐶. And then the angle we’re talking about is this enclosed angle here.

Now remember three hundred and sixty degrees is a full turn like that. If we do half a turn, we get a hundred and eighty degrees. And if we do quarter of a turn, we get ninety degrees. And no turn at all is zero degrees.

Angles in between zero and ninety are acute, angles in between ninety and a hundred and eighty degrees are obtuse, and angles between a hundred and eighty and three hundred and sixty are reflex.

Now the angle we’ve been given here is obtuse; it’s bigger than ninety degrees but it’s not quite as big as a hundred and eighty degrees.

Now the fact that it’s bigger than ninety degrees means it can’t be angle “𝐵”. The fact that it’s not as big as a hundred and eighty degrees means it can’t be “𝐶”, which leaves us with “𝐴”, and that looks like about a hundred and twenty-six degrees. So our answer is “𝐴”, one hundred and twenty-six degrees.

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